During the last century, the common reed (Phragmites australis) has spread through the North American continent following the introduction of a competitive Eurasian genotype. This invasion is problematic because marshes invaded by the common reed do not conserve a diverse flora and fauna. The southern part of the province of Quebec is also invaded by the common reed, but especially since the 1960s, i.e., since the beginning of the development of its highway system. There is very little information about landscape characteristics facilitating the establishment and spread of the common reed along roads. In this study, we mapped the common reed populations located along roads of a large region (1400 km2) of southern Quebec. Logistic regression models were performed to identify the main factors influencing the common reed. The road type is the most important variable of the models in agricultural or forest landscapes. Road ditches located on surface deposits with low drainage capacity (organic or clay) are more heavily invaded by the common reed than those located on rock, till or sand deposits. Consequently, a major road (national or regional) is more likely to be invaded by the common reed than a local road, especially if the road is located on organic or clay surface deposits. This study also shows that a large road receives more light energy than a narrow road, which favours a heliophilous plant like the common reed. The spread of the common reed along roads could be controlled by the use of shade structures (trees or shrubs planted along roads) which compete with the invasive plant for light.
Nomenclature : Marie-Victorin, 1995.